Justice Department: 4 U.S. citizens have been killed in drone strikes

5/22/13 4:31 PM EDT

The Obama administration has killed four U.S. citizens in drone strikes, the Justice Department said in new revelations Wednesday, ahead of President Obama's major national security speech set for Thursday at the National Defense University in Washington.

Attorney General Eric Holder's letter, obtained by POLITICO and addressed to Senate Judiciary Committee Chairman Pat Leahy (D-Vt.), includes justification for the administration's targeted killing of Anwar al-Awlaki, a U.S. citizen who was involved with Al Qaeda in Yemen. Obama had confirmed Awlaki's death soon after it happened in September 2011, but the administration had not, until Wednesday, confirmed that the killing was carried out by American forces in a drone strike.

The letter, first reported on by The New York Times, also listed three other Americans killed in drone strikes: Awlaki's son Abdulrahman al-Awlaki, Samir Khan and Jude Kenan Mohammed. They "were not specifically targeted by the United States," Holder said.

Obama also plans to announce that he will restart transfers of detainees out of Guantanamo Bay, the Wall Street Journal reported, citing U.S. officials. That's something he'd indicated would take place when he renewed his pledge to close the facility in remarks earlier this year. Obama isn't planning to offer much detail in his speech Thursday, though officials told the Journal that Obama would lift the ban on sending detainees to Yemen.

The White House would not confirm the report, though an official did say that the president would use his speech to "reiterate his strong commitment to closing the detention facility at Guantanamo as a part of our effort to align our counterterrorism strategy with our values." He will "announce a number of specific steps to advance that goal," the official said, without offering more information. More than 100 of the 166 detainees at Guantanamo are on hunger strikes, and 86 — including 56 from Yemen — have been approved for transfer out of the facility.

Obama will also use his speech to speak about the "legal and policy rationale" for the administration's use of drones, outlinging why the "use of drone strikes is necessary, legal, and just," the White House official said.

In his letter Wednesday, Holder detailed at length the administration's justification for targeting Awlaki, linking him to the attempted 2009 Christmas Day bombing of a U.S.-bound plane and to a 2010 plot targeting cargo planes headed to the United States.

There is even more “information that remains classified to protect sensitive sources and methods [that] evidences Awlaki’s involvement in the planning of numerous other plots against U.S. and Western interests and makes clear he was continuing to plot attacks when he was killed,” Holder said. Thus, the decision to target him "was lawful, it was considered and it was just," the attorney general added.

Holder said the letter is "only one of a number of steps the administration will be taking to fulfill the president's State of the Union commitment to engage with Congress and the American people on our counterterrorism efforts."

The speech comes as Obama signs new Presidential Policy Guidance that, Holder said, "institutionalizes the administration's exacting standards and processes for reviewing and approving operations to capture or use lethal force against terrorist targets outside the United States." The document will remain classified, but members of relevant congressional committees will be briefed on the policies in the days ahead.

Obama's speech will also touch on his renewed efforts to prevent attacks like the one that took place last year at a U.S. diplomatic facility in Benghazi, Libya, the White House official said. The president will detail "our broader strategy, including diplomatic and assistance efforts around the world, and how we can better secure our diplomatic facilities while remaining engaged in dangerous regions."

He will also "discuss how to balance securing our country and protecting our civil liberties at home," the official said.